Methacrylic resin has been widely used for automobile parts, optical components and the like because it has excellent optical properties in combination with remarkable weather resistance and high mechanical properties. These parts and components are required to have high transparency and chromaticity.
Examples of methods for producing methacrylic resin include bulk polymerization, solution polymerization and suspension polymerization methods. Generally, in order to produce methacrylic resin with excellent transparency and less impurities, bulk polymerization and solution polymerization are preferably used, but suspension polymerization has now been frequently used because it is easy to change varieties and thus suitable for the production of a wide variety of products in small quantities.
Conventionally, in the case of producing methacrylic resin with a suspension polymerization method, polymeric dispersants such as polyvinyl alcohol or poor water solubility inorganic salts such as calcium phosphate, hydroxyapatite, and magnesium pyrophosphate have been used as a dispersion stabilizer.
However, the use of methacrylic resin particles produced using a polyvinyl alcohol or an inorganic salt for the production of an optical component such as a film usable for a liquid crystal display or a light guide plate causes the dispersant incorporated in the fine particles of the resin to raise problems such as clouding, yellowing, or fish eyes. That is, in the field of optics where high transparency is required, a resin produced using a conventional dispersant cannot be used. A dispersant has been, therefore, desired, which does not impair the original transparency of a resin when shaped and contributes to the stable production of particles upon suspension polymerization.
Upon production of resin for optical applications with a suspension polymerization method, the use of sodium p-styrenesulfonate as a dispersant has also been known, but is not suitable for optical applications where excellent chromaticity is required because the resulting resin colors to yellow (for example, see Patent Literature 1 below).